The invention relates to a method and an arrangement for checking the effectiveness of measures for heating a catalytic converter in the exhaust gas of an internal combustion engine.
A rapid attainment and maintaining of the operating temperature of a catalytic converter is required in the interest of an optimal conversion of toxic constituents in the exhaust gas of an internal combustion engine.
Various measures are known for accelerated heating of the catalytic converter. Examples are: an increase of the exhaust-gas temperature by retarded ignition; a mixture enrichment in combination with blowing in secondary air; and, the use of a glow plug in the exhaust-gas system forward of the catalytic converter. This glow plug is intended to ignite and maintain the reaction of the secondary air, which is blown in rearward of the outlet valves of the engine, with the hydrocarbon constituents in the exhaust gas. The charge pressure control valve can be opened for a rapid warming of the catalytic converter in engines having exhaust-gas turbocharging and a charge pressure control valve. This clearly effects an earlier start of the toxic substance conversion in the catalytic converter, especially in combination with secondary air operation. This effect results from the situation that, for an opened pressure control valve, the exhaust gas is guided, to a certain extent, past the turbocharger. For this reason, hardly any energy is converted in the turbine of the turbocharger and the reaction of hydrocarbons and secondary air can take place undisturbed up to the catalytic converter via the open pressure control valve. Stated otherwise, an extinguishment of the secondary air flame in the chambers of the turbine wheel of the turbocharger does not take place.
An exhaust-gas system having an exhaust-gas flap and a cooling loop is known from European patent publication 0,937,869. In such an arrangement, the cooling loop can be closed for a cold engine or for a cold catalytic converter with an exhaust-gas flap or can be short circuited so that exhaust gas can no longer flow through the catalytic converter. This facilitates a rapid heating of the catalytic converter. At a higher exhaust-gas temperature, there is a flow through the cooling loop to cool the exhaust gas.
These measures for accelerated heating of the catalytic converter thereby influence the quality of the exhaust gas. Because of statutory requirements, the effectiveness of these measures has to be checked in motor vehicles having on-board means.
The invention defines a teaching for checking the effectiveness of the above measures.
More specifically, it is an object of the invention to provide a method of checking the effectiveness of at least one of the measures M for heating a catalytic converter in the exhaust gas of an internal combustion engine.
In the method of the invention, an index Tact for the temperature increase of the catalytic converter after activating at least one measure is determined by evaluating at least one signal SA which is detected in the exhaust-gas system of the engine; an expectation value Tmodel is determined for the increase of the temperature of the catalytic converter at least from operating characteristic variables of the engine and a temperature model; and, the index Tact is compared to the expectation value Tmodel and wherein at least a heating measure is taken as ineffective when Tact is clearly less than Tmodel and Tmodel was formed under the assumption of an effective heating measure or wherein at least one heating measure is judged to be ineffective when Tact is not clearly less than Tmodel and Tmodel was formed under the assumption of an ineffective heating measure.
The arrangement of the invention is for checking the effectiveness of at least one measure (M) for heating a catalytic converter in the exhaust-gas system of an internal combustion engine. The arrangement includes: means for activating the at least one measure (M); means for detecting a signal (SA) in the exhaust-gas system of the engine; means for evaluating the signal (SA) to determine an index (Tact) for an increase in temperature of the catalytic converter after activating the at least one measure (M); means for detecting operating characteristic variables of the engine; the evaluating means including means for determining an expectation value (Tmodel) for the increase in the temperature from the operating characteristic variables of the engine and a temperature model; the evaluating means also including means for comparing the index (Tact) to the expectation value and for evaluating the measure (M) as ineffective when the index (Tact) is clearly less than the expectation value (Tmodel) with the expectation value (Tmodel) having been formed under the expectation of an effective heating measure or, evaluating at least one heating measure as being ineffective when the index (Tact) is not clearly less than the expectation value (Tmodel) with the expectation value (Tmodel) having been formed under the assumption of an ineffective heating measure.
It is especially advantageous that the invention disclosed herein is not limited to a diagnosis of individual components but provides a complete system diagnosis.
Making the signal SA available via a temperature sensor affords the advantage of a precise detection of the catalytic converter temperature and this fact has positive effects on the reliability of the method.
The alternative formation of the signal SA from a signal as to the convertibility of the catalytic converter affords the advantage that a temperature sensor is not needed. The start of the conversion capability, which begins with increasing catalytic converter temperature, is determined and a conversion start, a specific temperature value, is assigned to the start of the conversion capability. Means for determining the conversion capability and therefore the conversion start are already available in modern motor vehicles. Methods for determining the conversion start are, for example, known from U.S. Pat. No. 5,675,967 which is incorporated herein by reference. The methods disclosed in this patent for determining the conversion start are included in the present disclosure.
An evaluation of the increase of the temperature can take place after a cold start or during a warm-up phase in the remaining operation. It is advantageous that the diagnosis is not limited to operating points which seldom occur but is instead, for example, possible in each operating cycle after a cold start.
Furthermore, the invention permits the ineffective heating measures to be identified with the aid of at least one further heat-up phase when several heating measures are used in parallel and the ineffectiveness of at least one heating measure is determined in a first heat-up phase. Here, the heating measure, which is assumed to be ineffective, is not activated and is identified in fact as ineffective when the actual temperature, which is determined in the further heat-up phase, is within a tolerance window to the actual temperature Tact determined in the first heat-up phase.
The use of the method is especially advantageous for the diagnosis of a glow device in the exhaust gas with the glow device being driven as part of a heating measure.
The advantage results from the situation that the glow device (for example, a glow device realized as a PTC resistance) is connected electrically in parallel to the secondary air pump. This situation makes an electrical diagnosis of the glow plug as an individual component difficult.
A similar advantage results in the use for diagnosing a charge pressure control valve in internal combustion engines having exhaust-gas turbocharging wherein the charge pressure control valve is driven as part of a heating measure.